Circuit arrangement for producing interrupted current for electrical spark apparatus

ABSTRACT

A discharge capacitor is connected in series circuit arrangement with a switching element across a spark gap and provides pulses of opposite polarity from pulses supplied to the spark gap by a power source via a resistor. A charging resistor is connected to a common point in the connection between the switching element and the discharge capacitor.

United States Patent Inventor Jan Hladik Nove Mesto Nad Vahom, Czechoslovakia Appl. No. 787,701 Filed Dec. 30, 1968 Patented Sept. 28, 1971 Assignee Vyskumny ustav mechanizacie a automatizacie Nove Mesto nad Vahom, Czechoslovakia CIRCUIT ARRANGEMENT FOR PRODUCING INTERRUPTED CURRENT FOR ELECTRICAL SPARK APPARATUS [50] Field of Search 315/240, 24S,163,160,173, 227,231, 312; 328/75 Primary Examiner-John W. Huckert A tmrney Richard Low ABSTRACT: A discharge capacitor is connected in series cir- 10 Claims 3 Drawing Figs cuit arrangement with a switching element across a spark gap US. Cl 315/240, and provides pulses of opposite polarity from pulses supplied 315/241 to the spark gap by a power source via a resistor. A charging Int. Cl 823k l/00, resistor is connected to a common point in the connection B23k 1/08 between the switching element and the discharge capacitor.

/7 2 4 500196! 0F a /2 $0006! 0/ UNI/7'6 P018219 .9 l8 5 06 MP5? CIRCUIT ARRANGEMENT FOR PRODUCING INTERRUPTED CURRENT FOR ELECTRICAL SPARK APPARATUS DESCRIPTION OF THE INVENTION The present invention relates to electrical spark apparatus, and more particularly to a circuit arrangement for producing interrupted current for electrical spark apparatus.

At the present time electrical spark apparatus may comprise electrical machining by electrical sparks. Initially, electrical spark machine tools were relaxation capacitive oscillators. The charge of the oscillator was accumulated in the capacitor for a specific period of time and the capacitor was discharged at considerably high current amplitude, in a short period of time, in a spark gap. A disadvantage of this type of spark generator is the dependence of the repetition rate or frequency of the spark discharges upon the space between the electrodes of the spark gap. This results in unstable operation of the spark generator. Another disadvantage of the aforedescribed spark generator is a relatively great loss of the electrode of the spark gap. Electrode losses have been reduced by the adjustment of optimum parameters of the spark generator. Such adjustment, however, is attained by comparatively complicated circuitry and difficult design requirements for the spark generator.

Other known types of spark generators include rotary generators, electron tube generators, thyratron generators, and semiconductor generators utilizing transistors and thyristors. These generators have the disadvantages of complexity and high cost.

The principal object of this invention is to provide a new and improved spark generator.

One object of the present invention is to provide a new and improved circuit arrangement for producing interrupted current for electrical spark apparatus.

Another object of the invention is to provide a spark generator which overcomes the disadvantages of known types of spark generators.

Still another object of the present invention is to provide a spark generator in which the repetition rate of the spark discharges is independent of the space between the electrodes of the spark gap.

A further object of my present invention is to provide a spark generator in which the repetition rate of the space discharges is variable to a very great extent.

One more object of this invention is to provide a spark generator in which electrode losses are reduced.

A further object of the present invention is to provide a spark generator in which the operating current is utilized at high efficiency.

Another object of the invention is to provide a circuit arrangement for producing interrupted current for electrical spark apparatus, which circuit arrangement is efficient, effective and reliable in operation.

Still another object of the present invention is to provide a spark generator with improved electrode positioning during operation.

In accordance with the present invention, a circuit arrangement for producing interrupted current for electrical spark apparatus having a spark gap, a source of DC power having a pair of opposite polarity terminals, a resistor connected in series circuit arrangement with the spark gap between the terminals of the power source whereby DC is supplied to the spark gap by the power source, comprises a discharge capacitor connected in series circuit arrangement with a switching element across the spark gap for providing pulses of opposite polarity from the DC supplied to the spark gap by the power source. A charging resistor is connected to a common point in the connection between the switching element and the discharge capacitor.

The discharge capacitor has a first plate terminal connected in common to the switching element and the charging resistor and.a second plate terminal connected to a common point in the connection between the spark gap and the first-mentioned resistor. The switching element comprises a thyristor. A source of timing pulses is connected to the thyristor for con trolling the conductivity condition of the thyristor. The charging resistor is connected between a terminal of the power source and the common point.

An additional source of DC power is provided having a higher DC voltage than the first-mentioned power source having one terminal connected to the corresponding terminal of the first-mentioned power source and a second terminal connected to the charging resistor in a manner whereby the charging resistor is connected between the common point and the second terminal of the additional power source.

The switching element comprises a thyristor having an anode connected in common to the first plate terminal of the discharge capacitor and the charging resistor, a cathode and a control electrode. The source of timing pulses is connected to the cathode and control electrode of the thyristor for con trolling the conductivity condition of the thyristor.

In one embodiment of the invention, an additional switching element is provided. An additional discharge capacitor is connected in series circuit arrangement with the second switching element across the spark gap for providing pulses. An additional charging resistor is connected between a common point in the connection between the additional switching element and the additional discharge capacitor and the second terminal of the additional power source. Each of the switching elements comprises a thyristor. The source of timing pulses is connected to each of the thyristors for controlling the conductivity condition of the thyristors. The first-mentioned thyristor has an anode connected to a common point in the connection between the first-mentioned charging resistor and the firstmentioned discharge capacitor, a cathode connected in common to the common-connected terminals of the power sources and to the source of timing pulses and a control electrode connected to the source of timing pulses. The additional thyristor has an anode connected to a common point in the connection between the additional charging resistor and the additional discharge capacitor, a cathode connected in common to the common-connected terminals of the power sources and to the source of timing pulses and a control electrode connected to the source of timing pulses.

The circuit arrangement of the present invention thus provides superposition on theDC crossing the spark gap of current peaks of reverse polarity. The current peaks are provided by the discharge capacitor via the thyristor, as described, so that the repetition rate of the spark discharges is independent of the space between the electrodes of the spark gap and is variable to a very great extent. The addition of the negative current peaks to the DC provided by the power source for the spark gap produces pulses spaced from each other in accordance with the discharge time of the discharge capacitor. This is advantageous because of the simplicity of structure of the circuit and the adjustability of the pulse repetition rate to an optimum for a specific current density in order to reduce electrode losses or consumption in the spark gap. The control of the spacing or gap between the electrodes of the spark gap and the control of the stability of the sparking process is improved in the circuit arrangement of the present invention due to the instant of discharge in the spark gap being determined by starting pulses of considerably greater voltage amplitude than that of the DC supplied by the power source. A signal which has a magnitude proportional to the space or distance between the electrodes of the spark gap is provided by the selection of the peak amplitude of the starting pulses. Such signal functions as an input quantity for varying the space between the spark gap electrodes.

In order that the present invention may be readily carried into effect, it will now be described with reference to the accompanying drawing, wherein:

FIG. I is a circuit diagram of an embodiment of the circuit arrangement of the present invention for producing interrupted current for electrical spark apparatus;

FIG. 2 is a circuit diagram of another embodiment of the circuit arrangement of the present invention; and

FIG. 3 is a circuit diagram of a modification of the embodiment of FIG. 2.

In these Figures, the same components are identified by the same reference numerals.

FIG. 1 discloses the spark generator or the circuit arrangement of the present invention for producing interrupted current for electrical spark apparatus. In FIG. 1, a source of DC power 1 comprises any suitable source of DC voltage such as, for example, a battery or an AC voltage source having a rectifier in its output. The DC power source 1 has a pair of opposite polarity terminals and lb. The positive polarity terminal is the terminal la and the negative polarity terminal is the terminal lb.

A resistor 2 is connected in series circuit arrangement with a spark gap 3 between the terminals la and lb of the DC power source 1 via a lead 4 from the terminal la to one end of the resistor, a lead 5 from the other end of the resistor to one electrode of the spark gap, and a lead 6 from the other electrode of the spark gap to the terminal lb. The DC power source 1 supplies a DC to the spark gap 3.

A switching element 7 of any suitable type such as, for example, a semiconductor controlled rectifier or thyristor, or the like, is connected in series circuit arrangement with a discharge capacitor 8 across the spark gap 3 and provides pulses of opposite polarity from the DC supplied to said spark gap by the DC power source 1. The switching element 7 is controlled in conductivity condition by timing pulses supplied by a source 9 of timing pulses.

The anode of the thyristor 7 is connected to a first plate terminal of the discharge capacitor 8 by a lead 11. The second plate terminal of the discharge capacitor 8 is connected to a common point 12 in the lead 5 connecting the resistor 2 and the spark gap 3, via a lead 13. The cathode of the thyristor 7 is connected to the terminal 16 of the DC power source 1 via a lead 14 and the lead 6. The control electrode of the thyristor 7 is connected to the source 9 of timing pulses via a lead 15. The source 9 of timing pulses is connected to the cathode of the thyristor 7 via a lead I6 and the lead 14.

A charging resistor 17 is connected between a common point 18 in the lead 11 connecting the thyristor 7 and the discharge capacitor 8 and the terminal la of the DC power source 1 via the lead 4. The circuit thus far described is identical in each of FIGS. 1, 2 and 3, with the exception of the connection of the charging resistor 17.

In the embodiment of FIG. 2, an additional or second source of DC power 19 comprises any suitable source of DC voltage such as, for example, a battery or an AC voltage source having a rectifier in its output. The second DC power source 19 has a positive polarity terminal 19a and a negative polarity terminal 19b connected to the negative polarity terminal lb of the first DC power source 1 via a lead 21. The second DC power source 19 provides a DC voltage which is more than five times higher than that of the first DC power source 1.

An additional switching element 22 is connected in series circuit arrangement with an additional discharge capacitor 23 across the spark gap 3 and provides pulses of opposite polarity from the DC supplied to said spark gap by the first DC power source I. The additional switching element 22 may comprise any suitable switching element such as, for example, a semiconductor controlled rectifier or thyristor, or the like. The additional switching element 22 is controlled in conductivity condition by timing pulses supplied by a source 9 of tim ing pulses.

The anode of the additional thyristor 22 is connected to a first plate terminal of the additional discharge capacitor 23 by a lead 24. The second plate terminal of the additional discharge capacitor 23 is connected to the common point 12 in the lead 5 connecting the resistor 2 and the spark gap 3, via a lead 25. The cathode of the additional thyristor 22 is connected to the common terminals lb and 19b of the first and second DC power sources 1 and 19, respectively, via a lead 26 and the lead 6. The control electrode of the additional thyristor 22 is connected to the source 9' of timing pulses via a lead 27. The source 9' of timing pulses is connected to the cathode of the additional thyristor 22 via the leads l6, 6 and 26.

An additional charging resistor 28 is connected between a common point 29 in the lead 24 connecting the additional thyristor 22 and the additional discharge capacitor 23 and the terminal 19a of the second DC power source 19 via a lead 31. The first charging resistor 17 is connected between the common point 18 in the lead 11 connecting the first thyristor 7 and the first discharge capacitor 8 and the terminal 19a of the second DC power source 19 via the lead 31.

The charge 0 of the second discharge capacitor 23, as is that of the first discharge capacitor 8, is the product of its capacitance C and its voltage V. The current i of the second discharge capacitor 23, as is that of the first discharge capacitor 8, during discharge, is the rate of change of the charge per unit time, or dQ/dt. The required current is also provided by decreasing the capacitance C of the discharge capacitor 23 or 8 and by increasing the voltage of the power source which charges the capacitor in proportion with the decrease in capacitance. The second DC power source 19 is provided to avoid the necessity for increasing the voltage of the first DC power source 1, since such increase in voltage would decrease the efficiency of operation of the spark generator due to an increase in losses in the resistor 2.

The source 9 or 9' of timing pulses may comprise any suitable pulse generator such as, for example, a blocking oscillator, a stable multivibrator, or the like. The source 9' of timing pulses may comprise, for example, a rectangular or square wave pulse generator 9a, which may comprise the source of timing pulses 9 of FIG. 1, and a pair of buffer circuits 9b and 9c for providing mutually phase shiftable timing pulses at the leads l5 and 27 Thus, a plurality of discharging circuits, each comprising a switching element and a discharge capacitor, may be connected in parallel with, or across, the spark gap 3, to provide higher efficiency of operation.

In the modification of the embodiment of FIG. 2, shown in FIG. 3, the additional switching element 22' and the additional discharge capacitor 23' are connected with the opposite polarities from those of the additional switching element 22 and the additional discharge capacitor 23 of FIG. 2. The pulses provided by the additional switching element 22 and the additional discharge capacitor 23' are therefore of the same polarity as the DC supplied to the spark gap 3 by the DC power sources 1 and 19.

In FIG. 3, the anode of the additional thyristor 22 is connected to a first plate terminal of the additional discharge capacitor 23' by a lead 24'. The second plate terminal of the additional discharge capacitor 23' is connected to the common terminals lb and 19b of the first and second DC power sources 1 and 19, via a lead 32, the lead 6 and the lead 21. The cathode of the additional thyristor 22' is connected to the common point 12 in the lead 5 connecting the resistor 2 and the spark gap 3. The control electrode of the additional thyristor 22' is connected to the source 9' of timing pulses via a lead 27'.

The additional charging resistor 28 is connected between a common point 29' in the lead 24' connecting the additional thyristor 22' and the additional discharge capacitor 23' and the terminal 19a of the second DC and the terminal 19a of the second DC power source 19 via the lead 31.

Current flows from the first DC power source 1 to the spark gap 3 via the resistor 2. A timing pulse from the timing pulse source 9 switches the thyristor 7 to its conductive condition, so that the discharge capacitor 8, which has been charged to a voltage determined by the difference in potentials applied thereto, is discharged via said thyristor. The discharge of the discharge capacitor 8 results in a voltage drop at the spark gap 3 which has a magnitude which is insufficient to maintain the discharge, and the spark in the spark gap 3 is extinguished. This increases the resistance of the spark gap 3 considerably, and the charging of the discharge capacitor 8 to the magnitude of the DC power source I commences.

As soon as the voltage of the discharge capacitor 8 exceeds the magnitude of the voltage required to maintain the discharge through the spark gap 3, the charge accumulated in said capacitor discharges into said spark gap. This causes the anode voltage of the thyristor 7 to become negative, so that said thyristor is switched to its nonconductive condition. A direct current thus begins to flow from the DC power source 1 through the resistor 2 and the spark gap 3. The discharge is properly initiated by a discharge of the charge of the capacitor 8 into the spark gap 3.

The current flows through the spark gap 3 until the next timing pulse is supplied by the source 9 of timing pulses. The current magnitude is determined by the voltage of the DC power source I, the resistance of the resistor 2 and the resistance of the spark gap 3. The current magnitude determines the capacitance of the discharge capacitor 8. The charging time constant of the discharge capacitor 8 via the charging resistor l7, and the switch-off time constant of the thyristor 7, together determine the maximum attainable frequency or repetition rate at which the source 9 of timing pulses may operate to produce the timing pulses.

An increase in the frequency or repetition rate is provided by the connection into the circuit of a plurality of series circuit arrangements, each comprising another switching element connected in series circuit arrangement with another discharge capacitor, and each series circuit arrangement being connected in parallel with the spark gap 3, the connection of two of such series circuit arrangements being as shown in FIG. 2. The thyristors are switched to their conductive condition by the timing pulses in the time sequence. The timing pulses alternately switch the thyristors 7 and 22 to their conductive condition.

As hereinbefore described, the second DC power source 19 is provided in FIGS. 2 and 3 to increase the efficiency of operation of the spark generator. Since the voltage level of the first DC power source 1 is considerably less than that of the second DC power source 19, the increase in efficiency results from the decreased amount of power consumed by the resistor 2 and the accumulation in the discharge capacitors 8 and 23 of a sufl'icient charge, without increasing their capacitance. The voltage of the second DC power source 19 is thus selected considerably higher than that of the first DC power source I.

The voltage of the first DC power source I may be increased to a magnitude slightly greater than the voltage at the spark gap 3 without disrupting the discharge of said spark gap after each interruption of said discharge. This may be accomplished by supplying starting pulses of the same polarity as the DC supplied by the power sources at the instant that the pulse of the opposite polarity from the DC supplied by the power sources ceases to flow through the spark gap 3 (FIG. 3). The advantage of supplying pulses of the same polarity as the DC supplied by the power source, in addition to supplying pulses of opposite polarity from that of the DC supplied by the power source, is the adjustability of the discharge time of the spark gap 3 and the intervals between discharges, if the positions of the spark gap electrodes are effectively regulated.

The current I flowing through the spark gap 3 of FIG. 1 during discharge is where V1 is the voltage of the first DC power source 1, V3 is the voltage of the spark gap 3 and R2 is the resistance of the resistor 2.

The magnitude of the voltage provided by the DC power source 1 of FIG. 1 must be greater than three times the voltage remaining across the spark gap 3 during the discharge. An increase in voltage improves the adjustability of the space between the electrodes of the spark gap 3. The capacitance of the discharge capacitor 8 is dependent upon the value of the current flowing through the spark gap 3 and the discharge current of said capacitor must be equal to, or slightly greater than, the current flowing said spark gap during the discharge, to permit the interruption of said discharge.

The discharge frequency of the spark gap 3 is limited by the charging and discharging time constants of the discharge capacitor 8, by switching the conductivity condition of the thyristor 7. This limitation is eliminated by the embodiment of FIG. 2, wherein the capacitance of the discharge capacitors and the charging and discharging time constants are decreased due to the utilization of the second DC power source 19.

As hereinbefore described, the voltage supplied by the first DC power source I must be decreased in order to decrease the losses in the resistor 2. In order to eliminate the adverse influence of such a decrease in voltage upon the reliable discharge or breakdown of the spark gap 3, and also upon the deterioration of control of the space between the electrodes of said spark gap, the instant of discharge is also determined by the discharge of the discharge capacitor charged to a higher voltage. Reliable discharge or breakdown of the spark gap 3 is provided by providing a second DC power source 19 voltage which is greater than twice that provided by the first DC power source 1, as hereinbefore described. When the reliability of the discharge at a greater space between the electrodes of the spark gap 3, is enhanced, the condition of control of such space is improved.

I claim:

1. A circuit arrangement for producing interrupted current for electrical spark apparatus having a spark gap, comprising a source of DC power having a pair of opposite polarity terminals, a resistor connected in series circuit arrangement with said spark gap between the terminals of said power source whereby a constant direct current is supplied to said spark gap by said power source, a unidirectional switching element, a discharge capacitor connected in series with said switching element, said switching element and discharge capacitor being connected across said spark gap in parallel with said power source, means for periodically actuating said switching means to superimpose a pulse on said spark gap of opposite polarity from the direct current supplied to said spark gap by said power source, and a charging resistor connected to a common point between said switching element and said discharge capacitor.

2. A circuit arrangement as claimed in claim I, wherein said discharge capacitor has a first plate terminal connected in common to said switching element and said charging resistor and a second plate terminal connected to a common point in the connection between said spark gap and the first-mentioned resistor.

3. A circuit arrangement as claimed in claim I, wherein said switching element comprises a thyristor, and further comprising a source of timing pulses connected to said thyristor for controlling the conductivity condition of said thyristor.

4. A circuit arrangement as claimed in claim 1, wherein said charging resistor is connected between a terminal of said power source and said common point.

5. A circuit arrangement as claimed in claim 1, further comprising an additional source of DC power having a higher DC voltage than said first-mentioned power source having one terminal connected to the corresponding terminal of said firstmentioned power source and a second terminal connected to said charging resistor in a manner whereby said charging resistor is connected between said common point and said second terminal of said additional power source.

6. A circuit arrangement as claimed in claim 2, wherein said switching element comprises a thyristor having an anode connected in common to the first plate terminal of said discharge capacitor and said charging resistor, a cathode and a control electrode, and further comprising a source of timing pulses connected to the cathode and control electrode of said thyristor for controlling the conductivity condition of said thyristor.

7. A circuit arrangement as claimed in claim 5, further comprising an additional switching element, an additional discharge capacitor connected in series circuit arrangement with said second switching element across said spark gap for providing pulses and an additional charging resistor connected between a common point in the connection between said additional switching element and said additional discharge capacitor and said second terminal of said additional power source.

8. A circuit arrangement as claimed in claim 5, wherein the series circuit arrangement of said additional discharge capacitor and said additional switching element provides pulses of the same polarity as the DC supplied to said spark gap by said first-mentioned power source.

9. A circuit arrangement as claimed in claim 7, wherein each of said switching elements comprises a thyristor, and further comprising a source of timing pulses connected to each of said thyristors for controlling the conductivity condition of said thyristors.

10. A circuit arrangement as claimed in claim 9, wherein said first-mentioned thyristor has an anode connected to a common point in the connection between the first-mentioned charging resistor and the first-mentioned discharge capacitor, a cathode connected in common to the common-connected terminals of said power sources and to said source of timing pulses and a control electrode connected to said source of timing pulses, and said additional thyristor has an anode connected to a common point in the connection between the additional charging resistor and the additional discharge capacitor, a cathode connected in common to the commoncom nected terminals of said power sources and to said source of timing pulses and a control electrode connected to said source of timing pulses. 

1. A circuit arrangement for producing interrupted current for electrical spark apparatus having a spark gap, comprising a source of DC power having a pair of opposite polarity terminals, a resistor connected in series circuit arrangement with said spark gap between the terminals of said power source whereby a constant direct current is supplied to said spark gap by said power source, a unidirectional switching element, a discharge capacitor connected in series with said switching element, said switching element and discharge capacitor being connected across said spark gap in parallel with said power source, means for periodically actuating said switching means to superimpose a pulse on said spark gap of opposite polarity from the direct current supplied to said spark gap by said power source, and a charging resistor connected to a common point between said switching element and said discharge capacitor.
 2. A circuit arrangement as claimed in claim 1, wherein said discharge capacitor has a first plate terminal connected in common to said switching element and said charging resistor and a second plate terminal connected to a common point in the connection between said spark gap and the first-mentioned resistor.
 3. A circuit arrangement as claimed in claim 1, wherein said switching element comprises a thyristor, and further comprising a source of timing pulses connected to said thyristor for controlling the conductivity condition of said thyristor.
 4. A circuit arrangement as claimed in claim 1, wherein said charging resistor is connected between a terminal of said power source and said common point.
 5. A circuit arrangement as claimed in claim 1, further comprising an additional source of DC power having a higher DC voltage than said first-mentioned power source having one terminal connected to the corresponding terminal of said first-mentioned power source and a second terminal connected to said charging resistor in a manner whereby said charging resistor is connected between said common point and said second terminal of said additional power source.
 6. A circuit arrangement as claimed in claim 2, wherein said switching element comprises a thyristor having an anode connected in common to the first plate terminal of said discharge capacitor and said charging resistor, a cathode and a control electrode, and further comprising a source of timing pulses connected to the cathode and control electrode of said thyristor for controlling the conductivity condition of said thyristor.
 7. A circuit arrangement as claimed in claim 5, further comprising an additional switching element, an additional discharge capacitor connected in series circuit arrangement with said second switching element across said spark gap for providing pulses and an additional charging resistor connected between a common point in the connection between said additional switching element and said additional discharge capacitor and said second terminal of said additional power source.
 8. A circuit arrangement as claimed in claim 5, wherein the series circuit arrangement of said additional discharge capacitor and said additional switching element provides pulses of the same polarity as the DC supplied to said spark gap by said first-mentioned power source.
 9. A circuit arrangement as claimed in claim 7, wherein each of said switching elements comprises a thyristor, and further comprising a source of timing pulses connected to each of said thyristors for controlling the conductivity condition of said thyristors.
 10. A circuit arrangement as claimed in claim 9, wherein said first-mentioned thyristor has an anode connected to a common point in the connection between the first-mentioned charging resistor and the first-mentioned discharge capacitor, a cathode connected in common to the common-connected terminals of said power sources and to said source of timing pulses and a control electrode connected to said source of timing pulses, and said additional thyristor has an anode connected to a common point in the connection between the additional charging resistor and the additional discharge capacitor, a cathode connected in common to the common-connected terminals of said power sources and to said source of timing pulses and a control electrode connected to said source of timing pulses. 